The invention concerns a method for accelerating the torque reduction of clutches in automatic transmissions.
Constantly increasing demands are being made at present on the functionality of automatic transmission: on one hand, more spontaneity is required, on the other hand, the clutches for different gear shifts are being repeatedly used to take into consideration the more compact design of the transmissions. Besides, the driver has a constantly increasing number of gears available to be shifted, the same as the possibility of manual engagement by the driver (tipp function). In addition, the driver must have the possibility of discontinuing or canceling gear shifts.
This results in the engagement and disengagement of the clutches is too slow or in engagement and disengagement at the right moment is becoming more and more difficult.
If, for example, a clutch is not filled enough and, nevertheless, has to become positively engaged at the next moment, this can lead to significant damage to the shifting quality. Conversely, considerable damages to shifting quality in automatic transmissions can result when a clutch takes up the torque too early or when the torque take-up lasts too long
According to the prior art, the above described problem is solved by the fact that prohibition times are introduced between the gear shifts. The effect of the prohibition times is that the clutch assumes a well-defined state such as xe2x80x9cclutch fullxe2x80x9d or xe2x80x9cclutch emptyxe2x80x9d.
Furthermore, discontinuation or the cancellation of gearshifts are prohibited or allowed only within a very limited scope. During torque build-up, the driving is usually at charge pressure whereby a torque take-up of long duration is produced by the follow-up control pressure.
Therefore, the problem on which this invention is based is to obtain as quickly as possible in a positively engaged clutch, a torque reduction and therewith a spontaneous reaction to the rotational speed of the engine.
However, despite the quick torque reduction, the clutch must remain at charge pressure in order to ensure the possibility of discontinuing or canceling gear shifts (immediate torque take-up).
Accodingly, it is proposed to accelerate the follow-up of the hydraulic pressure and thus the torque reduction by an over-compensation of the control in a positively engaged clutch.
According to the invention, this is achieved by driving the pressure control below the charge pressure level. The torque reduction is accordingly carried out quickly due to the increased pressure difference.
After a certain applicable time over an applicable pressure ramp, it is then returned again to filler pressure in order, by the pressure difference, to ensure or produce the immediate torque take-up again.
For the case that a change of shifting condition or a discontinuation of the shifting operation is carried out, or when the gear shift is canceled, the control abandons the controlled opening pressure. According to the invention, in this case an applicable pressure pulse is controlled in order, by the increased pressure difference, immediately to set the clutch again at charge pressure level so that the torque take-up be ensured. This can also occur by take-up of the time-dependent rapid filling.